The internal combustion engine conventionally includes an intake manifold to provide the air or air-fuel mixture to the cylinders. Coupled to the intake end of the intake manifold is a throttle body that controls manifold pressure and air flow to the cylinders. The air enters the intake end of the intake manifold and flows into a plenum. The air exits the plenum and enters the intake ports of the cylinders by way of a plurality of intake runners. In the case of Port Fuel Injection (PFI) engines, the fuel is injected at the intake ports. In the case of Direct Injection (DI) engines, the fuel is directed into the combustion chamber.
While providing necessary functionality, the intake manifold of the internal combustion engine is one of the dominant sources of engine radiated noise. The intake manifold radiates noise, vibration and harshness (NVH) from the surfaces of its plenum and intake runners.
Various designs have been undertaken to reduce NVH created by the intake manifold during engine operation by reducing radiated noise. For example, internal and external bracing has been incorporated to provide a reduction of noise radiating from the manifold's surface and to provide strength, thereby allowing for increased pressure while preventing manifold failure under a backfire condition. To compensate for the reduction of interior space caused by external bracing, the size of the intake manifold has been increased to compensate for the reduction in flow area. However, a larger manifold increases both product cost and weight while also complicating packaging.
Additional efforts to reduce NVH have included increasing the thicknesses of both the plenum and intake runner walls and by adding ribs to one or both of the plenum and the intake runners. Generally, plastic intake manifolds have rib patterns to increase the structural stiffness and reduce the radiated noise.
However, the benefits of such measures are limited by weight and manufacturing and, as a consequence, their inclusion may increase the weight, cost, and complexity in forming the intake manifold beyond acceptable targets. Accordingly, the NVH benefit derived from the use of ribs is limited to a certain frequency range (f<fmax=c/L, where c is the speed of sound, and L the distance between the ribs).
Accordingly, known approaches to reducing NVH in intake manifolds do not always produce satisfactory results. As in so many areas of vehicle technology, there is always room for improvement related to intake manifold designs having reduced NVH.